The invention relates to an arrangement for coating substrates.
In numerous etching and coating processes plasmas are generated out of which ions are accelerated onto a substrate. In order to be able to control the thickness of layers or the depth of etching, a dc voltage is provided between two electrodes which enclose a plasma.
If electrically non-conducting layers are to be deposited on a substrate, instead of a dc voltage an ac voltage must be applied in order to build up a dc potential at the substrate, which is required for the acceleration of charged particles, in particular of ions, in the direction toward the substrate.
For the coating or etching effect the generation of a stationary potential difference between plasma and electrode is essential, which in the case of a HF voltage applied at the electrode is achieved such that during the positive half period significantly more electrons can stream onto the electrode surface than positive ions can escape from it during the negative half period. But since averaged over time an identical quantity of positive and negative charge carriers are carried out of the plasma, the electrode becomes negatively charged relative to the plasma until almost throughout the entire length of both periods positive ions can stream in. Positive space charge regions leading to a rectifier effect are generated near the electrodes and lead to the formation of a barrier layer capacitance (cf. DE 37 08 717, column 5, line 20 to column 6, line 6).